Methods and systems for controlling gas turbine clearance

Abstract

Systems and methods for controlling the clearance in a gas turbine are provided. A temperature of a shaft of the gas turbine may be determined, and a desired temperature of an inner turbine shell of the turbine may be determined based upon the temperature of the shaft. The desired temperature of the inner turbine shell may be associated with a turbine clearance at which the gas turbine may be ignited. The temperature of the inner turbine shell may be altered by controlling the temperature of a gas that is circulated within the inner turbine shell, and a determination may be made that the temperature of the inner turbine shell exceeds the desired temperature. The gas turbine may be ignited subsequent to the determination that the temperature of the inner turbine shell exceeds the desired temperature.

1. A method for controlling ignition clearance in a gas turbine, the method comprising:
 determining, by a control unit comprising at least one computer processor, a temperature of a shaft of the gas turbine; 
 calculating, by the control unit based upon the determined temperature of the shaft, a desired temperature of an inner turbine shell of the turbine, wherein the desired temperature is associated with a turbine clearance at which the gas turbine may be ignited; 
 altering, by the control unit, a temperature of the inner turbine shell by controlling the temperature of a gas that is circulated within the inner turbine shell; 
 determining, by the control unit, that the temperature of the inner turbine shell exceeds the desired temperature; and 
 igniting, by the control unit, the gas turbine subsequent to the determination that the temperature of the inner turbine shell exceeds the desired temperature. 
 
     
     
       2. The method of  claim 1 , wherein determining a temperature of a shaft comprises determining a bulk temperature of the shaft based upon at least one of a predefined model or an equation. 
     
     
       3. The method of  claim 1 , wherein calculating a desired temperature of an inner turbine shell comprises calculating the desired temperature as a function of the determined temperature of the shaft. 
     
     
       4. The method of  claim 1 , wherein determining that the temperature of the inner turbine shell exceeds the desired temperature comprises:
 receiving, by the control unit from a thermocouple measuring device, a temperature measurement for the inner turbine shell; 
 comparing, by the control unit, the received temperature measurement to the desired temperature; and 
 determining that the temperature of the inner turbine shell exceeds the desired temperature based upon the comparison. 
 
     
     
       5. The method of  claim 1 , wherein controlling the temperature of a gas that is circulated within the inner turbine shell comprises controlling the temperature of a gas that is circulated within a closed-loop system. 
     
     
       6. The method of  claim 1 , further comprising:
 directing, by the control unit subsequent to the determination that the temperature of the inner turbine shell exceeds the desired temperature, the ventilation of the gas turbine; 
 determining, by the control unit, the temperature of the shaft subsequent to the ventilation; and 
 re-calculating, by the control unit, the desired temperature of the inner turbine shell. 
 
     
     
       7. The method of  claim 6 , further comprising:
 altering, by the control unit, a temperature of the inner turbine shell by controlling the temperature of a gas that is circulated within the inner turbine shell; and 
 determining, by the control unit, that the temperature of the inner turbine shell exceeds the re-calculated desired temperature, 
 wherein igniting the gas turbine comprises igniting the gas turbine subsequent to the determination that the temperature of the inner turbine shell exceeds the re-calculated desired temperature. 
 
     
     
       8. The method of  claim 1 , further comprising:
 calculating, by the control unit subsequent to the ignition of the gas turbine, a current clearance between a turbine blade and a casing of the gas turbine; 
 determining, by the control unit, that the calculated current clearance is outside of a predetermined clearance threshold; and 
 altering, by the control unit, the clearance of the gas turbine by controlling the temperature of the gas that is circulated within the inner turbine shell. 
 
     
     
       9. The method of  claim 8 , wherein calculating the current clearance comprises:
 determining a current operating condition and a current operating temperature of the gas turbine; 
 calculating a mechanical growth and a thermal growth of the gas turbine based on the current operating condition and the current operating temperature; and 
 adjusting a predefined initial clearance of the gas turbine based on the calculated mechanical growth and the calculated thermal growth. 
 
     
     
       10. The method of  claim 9 , wherein calculating a mechanical growth and a thermal growth comprises calculating at least one of a mechanical growth and a thermal growth of the shaft, a mechanical growth and a thermal growth of a turbine blade of the gas turbine, a thermal growth of a shroud of the gas turbine, or a thermal growth of a casing of the gas turbine.